Power systems for powering motors may comprise a plurality of components, such as one or more power generation units, drives line-ups, energy storage modules and a main bus to which the aforementioned components are connectable. For reasons of safety, such systems may be designed with redundancy. This is important in e.g. marine applications, where for example in some applications it is essential that dynamic positioning of a vessel to maintain its position by using its propellers and thrusters can be guaranteed at all times.
For the purpose of redundancy, the main bus may comprise several bus sections, with each section having or being associated with a respective set of power generation units, drive line-up, and energy storage module. A drive line-up is a unit comprising a drive line-up DC bus and one or more drive units connectable to the drive line-up DC bus. Depending on the type of fault, a plurality of strategies may be applied in a fault situation. A faulty section may for example be disconnected from the healthy portion of the power system in the event of a main bus short circuit fault. According to one strategy, the local energy storage module may be controlled to feed the drive line-up of the faulty section in case additional power should be transferred to that drive line-up.
In a power system, tying sections together on the DC link level, i.e. at the internal drive line-up DC bus level, is a challenge due to the demands this places on the protective devices tying them together. Also, in the case of distributed energy storage banks it is not as easy to use “load factor” between banks to reduce the aggregate size of the banks. This results in oversized energy storage banks.
An example of a DC power system for marine vessels is disclosed in US 2004/0102109 A1. The DC power system comprises a DC propulsion power distribution unit comprising a plurality of main drive generators, each one connected to a respective rung coupled to two DC rails. The system further comprises a weaponry power distribution unit including two DC rails coupled to a plurality of rungs, each being coupled to a respective directed energy weapon. Each rung of the weaponry power distribution unit is coupled to a rung of the DC propulsion power distribution unit through DC-DC converters. An energy storage device, such as a superconducting magnetic energy storage device, is coupled to each rung of the weaponry power distribution unit. The energy storage device supplies high-intensity power bursts to the directed energy weapons.
As previously mentioned, energy storage banks are generally oversized/over-dimensioned. The price in kWh of an energy storage bank is very high, and has impact on the overall power system cost, resulting in the need of high capital investment and low flexibility in system design.